1. Field of the Invention
The present invention relates to a re-combustion means for an alcohol engine having valves adapted to be opened and/or closed by virtue of electromagnetic force.
2. Description of the Prior Art
More and more attention has been paid to alcohol engines since the environmental pollution due to exhaust gas discharged from engines became a social issue. Namely, as a fuel alcohol contains less carbon compared to gas oil and gasoline, and an alcohol engine using alcohol as a fuel is characterized in that the amount of carbon dioxide gas and carbides contained in exhaust gas discharged therefrom is remarkably small compared to the amount of those contained in exhaust gas discharged from engines using gasoline, gas oil or the like as a fuel.
However, the latent heat for vaporization of alcohol is higher than that of gasoline; gasoline requires a vaporization latent heat of 0.7% of fuel heat value, while alcohol requires a vaporization heat of 5% of fuel heat value. This means that alcohol fuel is difficult to vaporize, and moreover it is the characteristics of alcohol fuel that alcohol fuel injected from an injection nozzle into compressed air in a combustion chamber tends to lower the temperature of the compressed air and the wall surface of the combustion chamber due to vaporization, the ignition of fuel so injected being thereby adverse by effected.
It is well known that in a conventional exhaust gas re-circulating means for an engine unburnt fuel contained in exhaust gas discharged from cylinders of the engine is retaken into the cylinders for combustion, while a part of exhaust gas is caused to be mixed with suction air, the generation of NOx being thereby controlled.
However, in the alcohol engine using alcohol as a fuel, combustion under partial load is extremely different from that under high load, and due to this the alcohol engine has drawbacks in that combustion becomes unstable under partial load, while a speed at which air-fuel mixture is generated becomes low under high load. In particular, in a compression ignition type reciprocating engine, an ideal compression ratio for a normal direct injection type engine is generally accepted to range from 15 to 17. In this case, the compression end temperature is around 650.degree. C., and when the engine has just been started, or air is cold, poor ignition and combustion occur, resulting in misfire or incomplete combustion. This tends to facilitate the generation of unburnt gas, producing odor or irritating odor inherent therein when it is discharged outside.
In particular, in a diesel engine employing alcohol fuel, since the temperature of the wall surface of the combustion chamber thereof is not high, when the engine is at low speed under low load, due to the high latent heat for vaporization of alcohol, the wall surface takes from fuel heat required for vaporization, and this prevents the promotion of vaporization of fuel, thereby making it difficult to produce vaporized air-fuel mixture.
In addition, when the engine is under partial load, the air-fuel ratio is great, in other words, fuel is lean, and if alcohol fuel is burned in this state, intermediate products such as formaldehyde, acetaldehyde and so forth are produced.
As a result, fuel is not completely burned at a low temperature, and the phenomenon in which unburnt gas is produced is very likely to occur, producing the odor or irritating odor inherent in unburnt gas. Moreover, the amount of hydrocarbon contained in exhaust gas becomes large, and poor ignition of fuel, i.e. poor starting-up of the engine is expected. Therefore, in the engine employing alcohol fuel, the amount of aldehyde to be discharged from the engine under partial load becomes large, and this causes a problem of producing the irritating odor, odor or the like. Thus, there are many problems to be solved with combustion conditions in a partial load area at a low temperature.
In addition, in regard to the engine employing alcohol fuel, the official gazette of Japanese Patent Laid-Open No. 67959/1983, for instance, discloses an alcohol reformed engine using reformed gas obtained by reforming alcohol with a view to purifying exhaust gas.
Furthermore, the official gazette of Japanese Utility Model Laid-Open No. 105052/1984, for instance, discloses a reformed gas engine using as a fuel reformed gas that is reformed from liquid fuel by means of a reforming means disposed at a certain position along the length of the engine exhaust passageway.